Refraction of light at an interface of two different media forms an essential basis in imaging and beam-shaping optics. While commonly viewed as a macroscopic phenomenon occurring at an interface of bulk media, at a microscopic level, the phenomenon involves diffractive transmission of light through atomic or molecular level scatterers (re-radiators) and subsequent interference among the produced wavelets.
An intrinsic connection is evident between refraction and grating diffraction in that both phenomena involve diffractive transmission and interference. Yet, their differences lie at the vastly different length scales involved. That is, refraction occurs due to the atomic/molecular level spacing of scatterers and grating diffraction occurs due to wavelength scale aperture spacing.
In the case of an interface with an artificial medium whose refractive index is negative, light can be bent to a negative angle with the surface normal. However, negative-index metamaterials commonly involve resonant structures designed at a sub-wavelength scale, and are intrinsically associated with loss and limited spectral width of operation. Additionally, in conventional gratings, the transmitted power is mostly carried by the 0th order diffraction (i.e., direct transmission), and other higher-order diffraction is usually of minor intensity. For example, the radiation pattern 12 of the conventional horizontal-dipole array 10 shown in FIG. 1a supports, the 0th order (direct transmission) as the primary beam.